Not applicable.
The present invention relates to tree felling heads, and in particular to a mechanism for rotating a tree felling head through a large angle relative to its mount in a lateral plane which is perpendicular to the cutting plane.
Heads for felling trees are well known for mechanized tree harvesting and generally include a relatively tall frame having hydraulically operated arms for holding a tree and a cutting mechanism such as a disc saw, shear or other cutting mechanism at the base of the frame for cutting off the tree. The arms are closed around the tree while it is being cut, and after it is cut, the arms sweep the tree rearwardly or to the side against the frame, typically over a butt plate which supports the bottom end of the tree, to hold the tree until it is unloaded. The felling head is typically mounted to a heavy duty vehicle, such as to the front of the boom of a swing-to-tree feller machine or to the front of a drive-to-tree machine.
The mounting of the head to the front of the machine typically provides for pivoting of the head relative to the machine in a plane which is lateral (side to side) and perpendicular to the plane of cut (the cutting plane). One such mount and a mechanism for rotating it are disclosed in U.S. Pat. No. 5,590,699. U.S. Pat. No. 5,590,699 discloses a high rotation mechanism having a pair of arc-shaped links 70, 72 pivotally connected to each other at an intermediary junction 76 and to the head at 74 and to a boom of a swing-to-tree feller buncher at 78. A hydraulic actuator 60 has its cylinder pivotally connected to the frame of the head and its piston pivotally connected to the intermediary junction. Thus, a single cylinder is used to provide a stated range of angles of xc2x190xc2x0 (a total of 180xc2x0) and over, although column 3, lines 58-61 indicates that it is perhaps better used at under 45xc2x0 (a total of 90xc2x0).
It is desirable that rotation mechanisms for felling heads have as high of a range of angular movement as possible. One reason for this is that when a tree is held by the head, it may be necessary to lay the tree down, particularly with a swing-to-tree feller buncher so that it lies generally parallel to a bundle of trees already cut or in a particular position. The higher that the head can pivot, the less that the machine must be driven from one location to another to place the tree in the desired location.
In addition, the rotation mechanism should have sufficient torque in the vertical position so as to counteract forces exerted on the head by trees being held and sufficient torque to guide the trees being held as they are placed parallel to a pile on the ground. Typical trees stand a considerable distance above the base of the head and the wind may be blowing. Therefore, it is important that, particularly in the vertical position of the head, maximum and balanced power is exerted on the head to maintain stability of the tree and head. At the extreme positions of the angular range of motion, the torque exerted on the head must be sufficient to manipulate the tree for precise placement, and also to return the head to the vertical position. In addition, the envelope of the head including the mechanism for rotating the head should not hamper the normal movement and manipulation of the head in the forest.
The invention provides a high rotation mechanism for a felling head which includes two pairs of links. The links of each pair are pivotally mounted to each other at an intermediary point, one end of each pair is pivotally mounted to the head and the other end of each pair is pivotally mounted to the pivot mounting structure relative to which the head is pivotable about a pivot axis. Each pair is driven by a separate hydraulic actuator which has one of its ends pivotally mounted to one of the links of each pair and its other end pivotally mounted to either the head or the mounting structure, but preferably the head. This mechanism is mounted to the head and pivot mounting structure so as to rotate the head in either direction from vertical in a lateral plane of rotation which is generally perpendicular to the cutting plane.
This construction can provide 220xc2x0 or more of total rotation in the plane of rotation. This is achieved by using two cylinders and skewing the torque curve of the crank/link mechanisms. At full rotation, one side loses torque and most or all of the torque exerted on the head comes from the opposite side cylinder. In the vertical position of the head torque is balanced in both directions and the torque is at or near its maximum. Torque is at or near its minimum in either extreme position of rotation.
The present invention also results in a design which has no exposed gears and no timing mechanisms, and which can be connected directly to the existing carrier vehicle hydraulics. All joints can be simple pin connections and the mechanism operates within a relatively stall envelope.